Interstitial cystitis is a poorly understood syndrome that includes pelvic pain, frequent urination and urinary urgency. There is increasing evidence that mature differentiated urothelial antigens and barrier functions are lost in patients with interstitial cystitis and in a spontaneous cat model of interstitial cystitis. We have developed a unique panel of biomarkers for different stages of urothelial differentiation. In these exploratory studies, we propose to perform the first systematic evaluation of urothelial differentiation in interstitial cystitis through the following Specific Aims: Aim 1: to evaluate the expression of biomarkers in urothelial cells taken from tissues. Normal urothelial cells will be harvested from urothelial tissues (bladder or ureter) and evaluated by flow cytometry, immunostaining, RT-PCR and Northern and Western blotting for expression of a panel of biomarkers. These studies will confirm the utility of the biomarker panel in defining specific stages of urothelial differentiation in situ. Aim 2: to study biomarker expression in urine samples. Urine samples will be collected from interstitial cystitis patients and normal volunteers. Evaluation of urothelial differentiation biomarker content will be performed. Soluble forms of the biomarkers in the urine will be evaluated by qualitative and quantitative immunoassay. Cells recovered from the urine sample will also be tested by immunostaining, immunoassay, and RT-PCR. Results of the biomarker assays will be compared to patient characteristics. These exploratory studies will develop a new series of biomarkers that may be informative for the diagnosis, patient stratification and effective use of treatment modalities for interstitial cystitis.